In pulse communication method, its frequency spectrum requires an extremely wide frequency band when rectangular pulses are used. The frequency band is expressed by 1/T [GHz] with the pulse width being T [ns]. Pulses with width T made of a sine wave with frequency f have secondary spectrums at intervals of 1/T centering around a spectrum with center frequency f and band width 2/T.
In order to avoid interference with other communication devices and to allocate frequency channels in a system, the band for the primary spectrum needs to be limited as well as for secondary spectrums. For a measure against these problems, the makeup disclosed in Japanese translation of PCT publication No. 2003-515974, for example, is known as a method used for a conventional pulse communication apparatus and system. FIG. 30 illustrates the makeup of a transmitting device in a conventional, pulse-using, ultrawideband (UWB) data transmission system, described in publication No. 2003-515974.
In FIG. 30, low-level impulse generator 4000 excites an optional, band-pass or pulse-forming filter 4002, by means of low-level impulses. Low-level impulse generator 4000 is composed of an arbitrary number of devices including a low-voltage step recovery diode (SRD), Zener diode, avalanche transistor, breakover device, and thyristor. Mixer 4008 actually works as a high-speed switch for adjusting the amplitude of signal output from oscillator 4006 according to impulse excitement from low-level impulse generator 4000.
The pulse envelope thus obtained retains the original time-domain shape in the impulse excitement. When filter 4002 is utilized, mixer 4008 actions so as to heterodyne (i.e. frequency-convert) a band-pass filtered or pulse shaped, low-level impulse signal, to a desired central operating frequency.
Next, the band width of a UWB signal in output from mixer 4008 is determined by that of band-pass or pulse-forming filter 4002. This method allows low-level impulse generator 4000 to actuate at a lower frequency, with the wide-band energy being shifted by a desired frequency.
The above-mentioned makeup aims at a pulse waveform for implementing a desired spectrum.
The conventional makeup, however, requires appropriately changing its characteristic in one-several tenths of 1 ns to implement a pulse shaper for shaping an extremely short impulse waveform, with a pulse width of 1 ns or shorter, for example, by means of a digital circuit. This may have been difficult to implement with the current IC manufacturing technology. With an analog circuit, a characteristic in the wide band from a direct current (DC) to several tens of gigahertz needs to be implemented with high reproducibility. With an analog circuit, the size of which is determined by the wavelength of the frequency component included in a signal, it may have been difficult to stably implement a miniature pulse shaper.